<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        div{
            width: 300px;
            background-color: rgba(0,0,0,0.3);
            padding: 10px;
            position: relative;
        }
        input{
            border: 0;
            padding: 10px 20px;
            width: 260px;
        }
        p{
            font-size: 12px;
            color: red;
            margin: 0;
        }
        img{
            position: absolute;
            right: 40px;
            top: 14px;
        }
    </style>
</head>
<body>
    <div>
        <input type="text" placeholder="请输入您的用户名">
        <img src="user.png">
        <p>用户名不能为空！</p>
    </div>

</body>
</html>
